Magnetic voltage reference device



y 1951 J. MONTNER EI'AL 2,983,862

MAGNETIC VOLTAGE REFERENCE DEVICE Filed Aug. 28, 1958 lo :4 l6 :8 24 2e,

2 Sheets-Sheet 1 UNSTABLE REGION X {AIR CORE INDUCTANCE lZ l, IXLI, lX l, IZI, R

E c (AVERAGE /CYCLE) /L s- HIGH LINE VOLTAGE l LOW LINE VOLTAGE FIG. 3

jDAMPED RINGING INVENTORS JOSEPH MONTNER ANDREW E. FLANDERS BY NEY May 9, 1961 Filed Aug. 28, 1958 FIG. 2

J. MONTNER ETAL MAGNETIC VOLTAGE REFERENCE DEVICE 2 Sheets-Sheet 2 FIG. 7

l (AVERAGE) R =l5.OK RB=|3 8K #MAX.=%E100,000 L (D I/ 5 o 2 1 o HG(COERCIVE FORCE) g A0 VOLTS, 60cPs 5 5 FIG. 5

z=x Lu 6 5 a 2 E z= RZXG g g NEGATIVE RESISTANCE E5 I i i MAX |AG f: UNSTABLE REGION l MAX E I z +x .w|-|EFE x =g f@9o POTENTIALL z UNSTABLE L| EAG(AVERAGE) FIG. 6

DC VOLTS INVENTORS JOSEPH MONTNER ANDREW E. FLANDERS BY ATTORNEY Ac VOLTS,6OCPS United States atent O MAGNETIC VOLTAGE REFERENCE DEVICE Joseph Montner, Whittier, and Andrew E. Flanders, La

Verne, Calif., assignors to General Dynamics Corporation, San Diego, Calif., a corporation of Delaware Filed Aug. 28, 1958, Ser. No. 757,842

3 Claims. (Cl. 323-61) This invention relates to a magnetic voltage reference device, and in particular to such a device employing solid state or static components.

Heretofore electronic voltage reference devices have been used with several distinct disadvantages. For example, electronic components used in such devices have a relatively short life as compared to solid state components thus requiring frequent replacement with a consequent interruption of the service rendered thereby. Moreover, electronic components are more expensive and accordingly the initial cost thereof is relatively high as compared to the cost of solid state or static components.

Static voltage reference devices are known and used but also incorporate certain disadvantages. Heretofore it has been impossible to obtain sufiiciently precise output voltage regulation with these known static voltage reference devices Where wide ranges of input voltages and frequencies are employed.

An object of this invention is to provide a magnetic voltage reference device which maintains its output voltage substantially constant over wide ranges of magnitude and frequency in its input voltage.

Another object of this invention is to provide a magnetic voltage reference device which maintains its output voltage substantially constant over wide ranges of magnitude and frequency in its input voltage by using a limiting circuit in the input to a saturable transformer, and a filter circuit in the output of the transformer.

Another object of this invention is to provide a magnetic voltage reference device which maintains its output voltage substantially constant over wide ranges of magnitude and frequency in its input voltage by using a limiting circuit which is responsive to the input voltage for generating fundamental and harmonic voltages in the input of a saturable transformer and by using a filter circuit in the output of the transformer for removing the generated harmonic voltages.

Other objects and features of the present invention will be readily apparent to those skilled in the art from the following specification and appended drawings wherein is illustrated a preferred form of the invention and in which:

Figure 1 is a schematic diagram of the circuit illustrating the teaching of this invention.

Figure 2 is a graph showing the hysteresis curve of typical rectangular looped core material.

Figure 3 is a representation of the waveform of a voltage produced in a portion of the circuit of Figure 1.

Figure 4 is a graphical representation of certain characteristics of the saturable transformer utilized in this invention.

Figure 5 is a further graphical representation of other characteristics of the saturable transformer utilized in Referring to Figure 1, there is illustrated the magnetic voltage reference device having an isolation circuit 11 comprising a resistor 14, a capacitor 16, and an inductor 18 in series arrangement having one end of the arrangement connected to input voltage terminal and the other end connected to one side of a capacitor 20. A limiting circuit 22 having an inductor 24 and a capacitor 26 in series is connected at one end with one end of the primary winding 28 of a magnetically saturable transformer St}, preferably having a rectangular hysteresis loop core material 3 2. The circuit 2 2 and winding 28 arrangement is connected across capacitor 20. In order to magnetically saturate core 32 in accordance with an input voltage the primary winding 28 is inductively disposed with respect to the core 32. The input terminals 10 and 12 are supplied with a suitable alternating voltage 13 of varying magnitude and frequency, the voltage thus supplied being of suflicient magnitude to effectively provide substantially complete saturation of the magnetic core 32. A secondary winding 33 is also inductively coupled to the core 32 to provide a voltage output. A frequency compensating circuit 34 having an inductor 36 in parallel arrangement with a capacitor 38 and a variable resistor 40 in series, has one end connected in series with one end of the secondary winding 33. A rectifier 42 has one of its input terminals connected to the other end of the frequency compensating circuit 34 and the other input terminal is connected to the other end of the secondary winding 33. One of the output terminals of the rectifier 42 is connected to one end of an inductor 44 which has its other end connected to one end of a parallel arrangement of a filter capacitor 46 and load resistor 43. The other output terminal of the rectifier 42 is connected to the other end of the capacitor 46 and resistor 48 arrangement. The output terminals of the voltage reference device are 50 and 52.

Referring to Figure 2, ideally, the maximum flux density of the core 3 2 of the transformer 30 would be fixed irrespective of the excitation current during saturation. However, the best available rectangular loo core material exhibits appreciable flux density change throughout the saturation region. Since excitation current is proportional to the magnetizing force H, a small relatively invariant amount of current is sufiicient to cause the flux change required throughout the body or central portion of the hysteresis loop. As the core saturates at 0 the magnetizing current rapidly increases from the value relative to the coercive force, H to some value determined by the associated circuitry and the voltage generator. The transition from high permeability flux change to saturation is not abrupt. When the magnetizing force exceeds field strengths greater than approximately 3H little ferro-magnetic induction remains. However, appreciable flux density change does occur throughout the entire saturation region. in other words, after saturation is reached, some voltage is transformed to the secondary of the transformer when additional voltage is applied to the primary. Therefore, a perfect output usually cannot be obtained. However, if the voltage applied to the transformer very rapidly reaches a current limit, it can cause no further change in flux and the flux is bounded. A fixed amount of saturation flux is thus added to the high permeability flux and a constant flux results.

By using the limiting circuit 22 of the present invention the voltage to the transformer is very rapidly applied to achieve the desired result. In the limiting circuit 22, the capacitor 26 allows very large magnetizing currents to flow once the transformer 30 has been saturated. The surge of current is absorbed by inductor 24 and stored in its magnetic field such that, on the alternate half-cycle, this bucks the line voltage for a finite period of time and then immediately reverses, supplying additional energy to the applied voltage, thus producing a square wave having high harmonic content, asshown in Figure 3. The square wave is used so that as the line voltage increases, the harmonic series of the high frequency order also increases. The regulation region begins approximately at the maximum squareness characteristic of the A.C. square waveform and continues with line voltage increase until asymmetry occurs between the positive and negative half cycles.

Referring to Figures 4 and 5, wherein the condition of asymmetry is graphically illustrated, it can be seen that a rectangular loop transformer presents rather unique characteristics. It is a coil with an iron core and is substantially dependent upon A.C. phenomena or bi-directional D.C. in its use. Referring more particularly to Figure 4, it can be seen that by virtue of its A.C. characteristics the transformer is an impedance but not in the conventional vectorial sense. Since the current is in phase with the voltage, it is somewhat resistive in nature. Thus, short of saturation, the primary offers resistive impedance, as designated by Z As soon as A.C saturation occurs, the coil takes on a predominately inductive characteristic. It will return appreciable energy to the circuit and is capable of oscillation. As the A.C. voltage is increased the impedance which is now reactive in nature rapidly goes to zero. When the impedance reaches zero, only D.C. resistance remains and high current may flow. Immediately the core completely saturates and air core inductance remains. The circuit becomes unstable, perhaps bi-stable, and asymmetry occurs. The voltage must now be reduced to some relatively low value before nominal action will take place. This is graphically illustrated more particularly in Figure 5. The low voltage point at which stable conditions return is dependent on the circuitry and is not necessarily at the value of A.C. saturation, E as shown.

It is to be noted that the device of the present invention operates in the potentially unstable region. Should either a voltage or current transient occur in this region, it may flip the core past the negative resistance boundary into the unstable region. As soon as asymmetry occurs the mode of operation is unstable and regulation is lost. The circuit parameters should be adjusted to keep the negative resistance boundary to a minimum. Practically this boundary is limited to a small portion of the potentially unstable region. Accordingly, the valve of the capacitor 26 is made as small as possible to assure firing the core 32 at minimum line voltage. The selected value of the inductor 24 determines the leading edge rise rate and the delay interval between each half of the A.C. square wave across the saturable transformer 36 and also serves to limit the rather large non-linear current loading on the voltage generator. Thus, the inductor 24 should be made as large as possible. Figure 6 illustrates the regulation obtained over a wide range of input voltages utilizing the limiting circuit 22 of the present invention.

Although the limiting circuit 22 largely controls the waveshape applied to the saturable transformer 30, a large amount of harmonic distortion in the voltage input line substantially affects the output of the saturable transformer 30. By incorporating the isolation circuit 11 there is obtained, first a low impedance source for the magnetic reference device and secondly, a filter which eliminates the undersirable harmonic distortion and thus provides greater Voltage output regualtion.

It is well known that a saturable transformer such as transformer 30 has an output voltage which is di ectly proportional to the frequency of the input voltage. Accordingly, if a constant frequency source of voltage is provided to the input of transformer 30, a fixed reference voltage is available at the output thereof. However, in the event the source frequency is not constant, frequency compensation must be utilized to obtain the desired fixed voltage output. In the device of the present invention frequency compensation is accomplished by providing the circuit 34 wherein the inductor 36 is of a very large value with respect to the apparent A.C. resistive load, the A.C. input voltage which rises at the rate of 6 db per octave as a function of frequency, decreases across the load resistance because of the high impedance of the inductor 36. (The decrease approaches approximately 6 db per octave.) However, frequency compensation by a very large inductor usually over compensates the transformer 30. In other words, the transformer 30 rejects all of the higher harmonic voltages to the point that it is over compensated and when the input voltage is increased the output voltage will decrease. To overcome this over compensation, the inductor 36 is by-passed by the series arrangement of the capacitor 38 and variable resistor 40, which determines the magnitude of the higher harmonics which are desired to be passed to the load resistor. The capacitor 38 is selected such that it is parallel resonant with the inductor 36 well above the fundamental, yet below the third harmonic. Figure 7 illustrates the regulation control obtained with adjustment of the resistor 40 to specific values.

While a certain preferred embodiment of the invention has been specifically disclosed, it is understood that the invention is not limited thereto as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims:

What we claim is:

1. A voltage reference device comprising input terminals for receiving an input voltage of variable magnitude and frequency, a saturable transformer having a magnetic core, a primary winding in inductive relationship with said core and connected to said terminals in series with an inductor and capacitor, and a secondary winding in inductive relationship with said core for producing an output voltage having fundamental and harmonic frequencies, said input voltage being of sufiicient magnitude to produce magnetic saturation of said core, and circuit means connected in series with said secondary winding, said circuit means comprising a parallel arrangement of inductor means and capacitor means, said parallel arrangement having parallel resonance at a predetermined frequency between said fundamental and harmonic frequencies and variable means in series with said capacitor means for adjusting the magnitude of said harmonic frequencies in said output Voltage to predetermined values, whereby the output voltage of said volt age reference device remains substantially constant even though the magnitude and frequency of said input voltage vary over wide ranges.

2. A voltage reference device comprising input terminals for receiving an input voltage of variable magnitude and frequency, a saturable transformer having a magnetic core, a primary winding in inductive relationship with said core and connected to said terminals in series with an inductor and capacitor, and a secondary winding in inductive relationship with said core for producing an output voltage having fundamental and harmonic frequencies, said input voltage being of sufficient magnitude to produce magnetic saturation of said core, and circuit means connected in series with said secondary winding, said circuit means comprising a parallel arrangement of inductor means and capacitor means, said parallel arrangement having parallel resonance at a predetermined frequency between said fundamental and harmonic frequencies and variable resistor means in series with said capacitor means for adjusting the magnitude of said harmonic frequencies in said output voltage to predetermined values, whereby the output voltage of said voltage reference device remains substantially constant even though the magnitude and frequency of said input voltage vary over wide ranges.

3. A voltage reference device comprising input terminals for receiving an input voltage of variable magnitude and frequency, a saturable transformer having a magnetic core, a primary winding in inductive relationship With said core and connected to said terminals in series with an inductor and capacitor, and a secondary winding in inductive relationship with said core for producing an output voltage having fundamental and harmonic frequencies, said input voltage being of sufiicient magnitude to produce magnetic saturation of said core, and circuit means connected in series with said secondary Winding, said circuit means comprising a parallel arrangement of inductor means and capacitor means, said parallel arrangement having parallel resonance at a predetermined frequency between said fundamental and harmonic frequencies, and a manually variable resistor in series with said capacitor means for adjusting the mag- 15 References Cited in the file of this patent UNITED STATES PATENTS 2,606,305 Court Aug. 5, 1952 10 2,668,942 Varela et al. Feb. 9, 1954 2,763,827 Evans Sept. 18, 1956 FOREIGN PATENTS 555,589 Great Britain Aug. 30, 1943 612,442 Great Britain Nov. 12, 1948 

